Martinkus was freed by his captors on Sunday after they Googled his name on the Internet to check if he was telling the truth about his affiliation with public broadcaster SBS.
SBS executive producer Mike Carey said Martinkus' captors investigated his background on the Internet to make sure he was not a contractor for the US or a CIA agent.
"They had thought he was working for the Americans as an informer. In this case, modern technology probably saved the journalist's life," Carey said.
Martinkus is a freelancer who has covered conflicts from East Timor to Iraq. He was grabbed at gunpoint outside the al-Hamra Hotel just across the road from the Australian embassy in Baghdad.
Martinkus was working on a news feature for SBS's Dateline program on rebel Shia cleric Moqtada al-Sadr and his Mehdi Army when he was nabbed.
The Internet has become a popular tool for Iraqi militant groups to broadcast their cause to the world.
For the past couple of months, the media and world organisations have tuned to Islamic Web sites for information on their latest captives. Some of these Web sites show videos of captured peoples' plea for safety as well as the live executions of unfortunate hostages.
Another worker was reported to be kidnapped today by terrorist Iraqi gunmen. Care worker Margaret Hassan was captured in Baghdad yesterday afternoon while on her way to work. She is employed by the Australian arm of CARE International and is the organisation's chief of operations in the war zone.